The present invention relates to a circuit arrangement with a digital controller for operating an electric motor, and to a corresponding method.
In electric motors, it is known that they require a considerably higher current after they have been switched on and during the running-up phase owing to the inductances of the motor windings. If the motor is driven by means of a digital controller, the control range of the controller must comprise both the normal operation and the running-up phase of the motor.
The object of the present invention is to specify a circuit arrangement with a digital controller which has increased control sensitivity during the normal operation of the motor, and to specify a corresponding method.
The circuit arrangement according to the invention switches the control range of the digital controller over into a higher current range for the running-up phase. Then, for the normal operation of the motor, the control range of the controller is switched back again into a lower current range. As a result, the control sensitivity of the controller is completely available for the normal operation of the motor. In addition, a high current is made available for a rapid start for the running-up phase.
The circuit arrangement can contain, for example, a special digital-to-analogue converter, whose sensitivity can be switched over by means of a control signal. In a further exemplary embodiment, a multiplexer is connected between the digital controller and a downstream digital-to-analogue converter. The digital-to-analogue converter has a higher resolution than the controller, with the result that the digital signals of the controller can be switched through to various ranges of the digital-to-analogue converter by means of the multiplexer.
A control signal is required to switch over between running-up phase and normal operation. This signal can be derived, for example, by means of a sensor which is already present, is arranged on the motor and generates the synchronization signals for controlling the motor and thus detects the speed of the motor.
Applications of the invention result, in particular, for video recorders, camcorders, and further domestic appliances with electric motors.